The luopan

A geomancer's instrument first

The usual telling has the compass invented for navigation and later borrowed by fortune tellers. The history runs the other way. The earliest Chinese magnetic direction finder, the south-pointing spoon (司南), dates to the Warring States and Han periods, and it was used for divination and for orienting tombs, halls, and cities. The freely pivoting magnetic needle came later, and only in the Song was it adapted to finding a heading at sea.

That order matters for reading the instrument. A luopan is not a navigation compass with mystical decoration added. It is a siting instrument that navigation later borrowed a component from.

What the parts do

• The heaven pool (天池): the small well at the center holding the needle. This is the only part that measures anything.
• The inner plate: the rotating disc carrying the printed rings, turned until the needle lines up with the marked meridian.
• The outer square with crossed threads: the frame is squared to the wall or facing being measured, and the threads read off the bearing.
• The rings (層): concentric bands printed with the eight trigrams, the 24 mountains, the 64 hexagrams, the 28 lunar mansions, and more, depending on the type.

A cheap luopan and an expensive one read the same bearing. What you pay for is more rings, better printing, and a needle that settles faster.

The ring that actually matters

For nearly all domestic work, one ring carries the weight: the earth plate 24 mountains (地盤正針). It divides the circle into 24 named sectors of 15 degrees each, and a building's sitting and facing directions are read from it. Everything this site computes for a building, including the whole natal chart library, keys off that single number.

A San He luopan prints three 24-mountain rings rather than one, each offset by 7.5 degrees and each assigned a job: the earth plate for sitting and facing, the human plate (人盤中針) for reading surrounding landforms, the heaven plate (天盤縫針) for water. Explanations for the offsets vary between lineages, and some tie them to historical magnetic declination. We report the disagreement rather than adjudicate it. A San Yuan luopan drops those extra rings and adds the 64 hexagrams, which is what Flying Star practice draws on.

Taking a bearing without one

You need the direction the front of the building faces, in degrees. Stand at the main door looking out, hold a phone compass level, and read the number. Then two cautions that matter more than the instrument:

1. Use magnetic north, not true north. The tradition was built on what a magnetic needle reads, so do not apply a declination correction. Phone compasses often default to true north, so check the setting.
2. Steel moves needles. Take the reading a few steps clear of the door frame, appliances, and reinforced walls, and take it more than once. Local metal will shift a reading by far more than declination ever would, and a shift of eight degrees can move you into the next mountain.

The honest note

The luopan is a genuinely sophisticated object and a real piece of the history of science, being among the earliest practical applications of magnetism anywhere. None of that makes the readings predictive. The needle finds magnetic north, which is a fact; the rings then map that bearing onto a symbolic system, which is tradition rather than measurement. Treating an accurate instrument as evidence for the system printed on it is the most common mistake made about this object.